#UserDefaultsExample

Author:		Johnny Slagle
Date:		Nov 1st, 2012

##Description

This is a very simple example project I created to demonstrate the proper way to store and load custom objects, from NSUserDefaults, using the methods encodeWithCoder and iniWithCoder.

##Understanding the Project

###JSPerson JSPerson is a very basic class that only contains the following two properties:

@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSString *number;

JSPerson implements initWithCoder:

- (id)initWithCoder:(NSCoder *)decoder {
    if((self = [super init])) {
        self.name = [decoder decodeObjectForKey:JSPersonNameKey];
        self.number = [decoder decodeObjectForKey:JSPersonNumberKey];
    }
    return self;
}

and encodeWithCoder:

- (void)encodeWithCoder:(NSCoder *)encoder {
    [encoder encodeObject:self.name forKey:JSPersonNameKey];
    [encoder encodeObject:self.number forKey:JSPersonNumberKey];
}

###JSTableViewController

JSTableViewController is the project's rootViewController is a simple UITableViewController. The data source for it's tableView is an array of JSPerson objects called persons which is lazy instantiation. It is defined as such:

@property (nonatomic, strong) NSMutableArray *persons;

JSTableViewController also stores an array of names that loads ~37 names from the plist Names.plist in the app bundle. A random name is selected when creating a new person. It's defined as such:

@property (nonatomic, strong) NSArray *names;

###Encoding & Decoding

JSTableViewController has the methods that should be looked at to understand how to store and load your objects.

####Storing Persons Array The method to see how to store an array in NSUserDefaults is called savePersons. It looks like this:

- (void) savePersons {
    // Save the persons array
    [[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:self.persons]
                                              forKey:JSPersonsArrayKey];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

It uses NSKeyedArchiver to archive your persons array into NSUserDefaults. The method archivedDataWithRootObject uses JSPerson's encodeWithCoder to create an NSData object.

####Loading Persons Array The loading of the potentially stored persons array is done in it's lazy instantiation method. It looks like this:

- (NSMutableArray *)persons {
    if(_persons == nil) {
        // Load the NSData back from the NSUserDefaults
        NSData *dataRepresentingSavedArray = [[NSUserDefaults standardUserDefaults] objectForKey:JSPersonsArrayKey];
        
        // Is there data there?
        if (dataRepresentingSavedArray != nil) {
            // Unarchive the NSData into an array.  This uses JSPerson's initWithCoder method to do so.
            NSMutableArray *oldPersonsArray = [NSKeyedUnarchiver unarchiveObjectWithData:dataRepresentingSavedArray];
            
            // Store as persons array if an array is unarchived
            if (oldPersonsArray != nil) {
                _persons = [[NSMutableArray alloc] initWithArray:oldPersonsArray];
            }
        } else {
            // Create an empty persons array
            _persons = [[NSMutableArray alloc] init];
        }
    }
    return _persons;
}

In this method we use the method unarchiveObjectWithData to load the data back from NSUserDefaults. When it does that, NSKeyedArchiver uses JSPerson's initWithCoder method to load the data back into a JSPerson object.